JPH0748451B2 - Method for manufacturing laminated plate for electret - Google Patents

Description

The present invention relates to a method for manufacturing an electret used in an earphone, a headphone, a microphone, or the like.

[Conventional technology]

BACKGROUND ART Conventionally, as a material for an electret used in an earphone, a headphone, a microphone or the like, a thermoplastic resin film capable of forming an electret, such as a tetrafluoroethylene resin or a tetrafluoroethylene-hexafluoropropylene copolymer film A laminated plate obtained by a method of depositing a metal is inexpensive and is commonly used as a film electret.

On the other hand, a metal sheet referred to as a back electret is coated with a fluororesin such as the above-mentioned tetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer or the like which can constitute the electret, or polycarbonate, polypropylene, etc. Electretization method (Japanese Patent Publication No. 21-21335, Japanese Patent Publication No. 528694, etc.), a method in which a metal sheet is contacted with a non-electretized polymer film and baked, and further electretized (Japanese Patent Publication No. 21-21334). Further, a method is proposed in which the above-mentioned fluororesin is uniformly attached to a metal sheet by printing, coating or spraying on a metal sheet, followed by drying and baking to form an electret (JP-A-59-101998). Has been done.

[Problems to be solved by the invention]

In the audio boom of recent years, the weight in which the back electret is used rather than the membrane electret is increasing due to advantages in terms of sound quality and sensitivity.

However, among the methods of manufacturing the back electret proposed above, Japanese Patent Publication No. 51-21335 and Japanese Patent Publication No. 52-8.
Since the method described in Japanese Patent No. 694 is a method of coating a resin, there is a problem that the film thickness lacks uniformity and smoothness, and there is a film defect such as a pinhole, so that the electrification deterioration after electretization is large. is doing. Further, Japanese Patent Publication No. 51-21334 discloses a method of using a film, but simple baking causes poor adhesion to a metal sheet.
There is a problem in reliability such as peeling under the use environment, and it is also impossible to control the film thickness. Since the method described in Japanese Patent Laid-Open No. 59-101998 is based on printing of a resin solution, etc., the film thickness uniformity and smoothness can be improved in the same manner as the methods of Japanese Patent Publication Nos. 51-21335 and 52-8694. It is inferior and has a film defect such as a pinhole, which causes a problem that the electrification deterioration after electretization is large. The conventional method as described above has a problem from the viewpoint of pursuing sound quality.

[Means for solving problems]

In view of such circumstances, as a result of intensive investigations by the present inventors to solve the above problems, while indirectly heating the thermoplastic resin film that can form the electret while heating only from the metal sheet side using a pressure bonding roll. Moreover, the method for producing an electret laminated plate having a film thickness reduction rate of almost zero, rich uniformity, and extremely excellent surface smoothness was completed by instantly press-bonding to a metal sheet.

That is, the present invention is a pressure roll composed of a pair of a heating roll and a roll not having a heating source, a metal sheet is supplied to the heating roll side, and a heat that can constitute an electret on the roll side having no heating source. While supplying the thermoplastic resin film, the metal sheet and the thermoplastic resin film are inserted between the rolls, the contact time between the metal sheet and the thermoplastic resin film and the roll is 1 to 10 seconds, and the contact band width is 1
The present invention provides a method for manufacturing an electret, which is characterized in that the laminated plate obtained by controlling the thickness to be 20 mm and thermocompressing the both is charged.

Hereinafter, the present invention will be described in more detail.

As the metal sheet used for carrying out the method of the present invention, any of aluminum, stainless steel, copper, titanium and alloys thereof can be applied.

On the other hand, the thermoplastic resin film is not particularly limited as long as it can form an electret favorably, for example, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro Alkoxyethylene copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETEF), tetrafluoroethylene polymer (PTF)
Fluorine resin films such as E) and films such as polypropylene and polycarbonate can be applied.

When using the metal sheet, a metal sheet that does not adhere to oils and fats is first used, and further, a base treatment is performed in order to improve the adhesiveness to the thermoplastic resin film. The base treatment is a treatment that does not increase the surface roughness of the metal base in order to achieve the uniformity of the thickness of the resin film and the smoothness of the surface, for example, the formation of a film by anodizing or chemical conversion treatment or the formation of a coupling agent. The method is not particularly limited as long as it is a method for utilizing or improving adhesion.

In heat-sealing the thermoplastic resin film and the metal sheet, a heating roll, for example, an induction heating roll having a heating source inside the metal roll and a roll not having the heating source, for example, a heat-resistant rubber roll typified by heat-resistant silicon or fluororubber A pressure bonding roll composed of a pair of is used. The pressure-bonding roll has a structure in which the contact band width between the rolls and between the metal sheet and the thermoplastic resin film can be controlled by appropriately changing the pressure applied between the rolls. The metal sheet is supplied to the heating roll side, while the thermoplastic resin film is supplied to the roll side having no heating source. Subsequently, the metal sheet and the thermoplastic resin film are inserted between the rolls. At this time, the thermoplastic resin film is indirectly heated from the heating roll through the metal sheet for a predetermined time for a predetermined width.
The contact time between the rolls and the metal sheet and the thermoplastic resin film is 1 to 10 seconds, preferably 1 to 3 seconds, and the contact band width, that is, the metal sheet or the like has a contact band width in the direction of feeding to the roll of 1 to 20 mm, preferably Is in the range of 5 to 15 mm. Contact time exceeds 10 seconds, or contact width is 20
If the thickness exceeds mm, the thickness of the film of the electret laminate for molding is greatly reduced because all the layers are melted in the thickness direction of the thermoplastic resin film, and the surface is also lacking in smoothness. The physical properties may change depending on the film. Also, the contact time is less than 1 second,
Alternatively, when the contact band width is less than 1 mm, the heat fusion is not sufficiently performed, and thus the adhesive force is insufficient.

The method of the present invention does not melt the entire thermoplastic resin film, but substantially fuses only the contact interface layer with the metal sheet, and more specifically, the melting of the thermoplastic resin film is the contact interface with the metal sheet. More than 50% of the film original thickness relative to the thickness direction of the film by heat fusion so as to keep the melting within 50%, the thickness of the thermoplastic resin film to be supplied hardly decreases even after lamination, In addition, it is possible to obtain a electret laminated plate having a uniform film thickness over the entire laminated plate, a smooth surface, and excellent adhesiveness.

The term “smoothness of the surface” as used herein means two aspects that the thermoplastic resin film layer is not only smooth, but that there is no entrapment of air or the like. The surface temperature of the heating roll may be appropriately selected depending on the type of the thermoplastic resin film used, and the temperature is kept within the condition range of -20 ° C to + 80 ° C from the melting point of the thermoplastic resin film. If the heating temperature deviates from the above temperature range, thermal fusion will not be sufficiently performed, resulting in insufficient adhesion and poor surface finish.

The electret laminate obtained by the method of the present invention is cut into a predetermined size, and then polarized and charged (electret) by corona discharge or the like, and then subjected to aging treatment, which is used for earphones, headphones or microphones. It

〔The invention's effect〕

As described above in detail, the present invention provides excellent adhesion between the metal sheet and the film, and also has extremely excellent uniformity and smoothness of the film layer, and the thickness reduction rate of the supplied film is almost zero. Since it is a method that can be controlled to the above, and an electret having excellent characteristics can be obtained, it is industrially valuable.

〔Example〕

Next, the method of the present invention will be described in more detail with reference to Examples of the present invention while comparing with Comparative Examples, but the method of the present invention is not limited to these Examples.

Example 1 An aluminum plate having a thickness of 0.5 mm (5052-H as a metal sheet
34 material) was used to perform degreasing with trichlorethylene using the plate as a base treatment. Continuing, specific resistance 500 × 10 ⁴ Ω
0.5% by volume of triethanolamine in cm ion-exchanged water
The aluminum plate was immersed in a weak alkaline aqueous solution of 95 ° C., which had been dissolved and adjusted to pH 10, for 5 minutes for chemical conversion treatment.

A tetrafluoroethylene-hexafluorofluoride (FEP) copolymer film (hereinafter referred to as FEP film) having a thickness of 25 μm and a melting point of 270 ° C. was prepared as a thermoplastic resin film. As the pressure bonding roll, a metal heating roll (roll diameter 250 mmφ) by an induction heating method was used as the lower roll, and a heat-resistant silicone rubber roll (roll diameter 250 mmφ) having no heating source was placed as the upper roll. The surface temperature of the heating roll
After setting to 350 ° C., the aluminum plate was supplied to the heating roll side of the lower roll, while the FEP film was supplied to the rubber roll side of the upper roll. Subsequently, the aluminum plate and the FEP film were simultaneously inserted between the rolls, the contact zone width between the aluminum plate and the FEP film and the roll was set to 5 mm, the contact time was set to 2 seconds, and the rolls were passed and thermocompression bonded. After allowing the resulting electret laminated sheet to cool naturally, the thickness of the FEP film layer was measured by a film thickness meter to be 24.5 μm, and the original thickness of the FEP film used was almost maintained. This FEP film thickness was evenly distributed over the entire surface of the obtained electret laminated sheet, and a smooth and beautiful surface was obtained without air entrapment.

The surface roughness of the surface was Ra = 0.20.

Next, the adhesive strength between the aluminum plate and the FEP film was measured by ASTM D-9
When measured according to 03-49, the film itself is 1200 g /
It was fractured under a load with an inch width, and it was confirmed that there was sufficient adhesion between the aluminum plate and the FEP film.

50 mm × a sheet of laminated plate for electret obtained in the same manner
After cutting to a size of 50 mm and polarization charging by corona discharge, aging treatment was performed at a temperature of 150 ° C. for 1 hour. Subsequently, the electretized laminated plate was
The residual potential was measured after exposure for 1000 hours in an environment of ℃ and relative humidity of 95%, but almost no charge decay was observed.

Example 2 A brass plate having a thickness of 0.5 mm (c2680-PH) as a metal sheet
Was degreased with an alkaline aqueous solution, and then immersed in a chromic acid solution at 50 ° C. for 1 minute for chemical conversion treatment.

Thermoplastic resin film with a thickness of 50 μm and melting point of 310 ° C, tetrafluoroethylene-perfluoroalkoxyethylene (PF
A) A copolymer film (hereinafter referred to as PFA film) was prepared.

The brass plate and the PFA film were thermocompression bonded under the same method and conditions as in Example 1 except that the surface temperature of the heating roll was set to 380 ° C. After allowing the obtained electret laminated sheet to cool naturally, the thickness of the PFA film layer was measured in the same manner as in Example 1 to find that it was 49 μm, and the original thickness of the film used was almost maintained. This film thickness was evenly distributed over the entire surface of the obtained electret laminate sheet, and a smooth and beautiful surface was obtained without air entrapment. The surface roughness of the surface was Ra = 0.15. Next, when the adhesive force between the brass plate and the PFA film was measured by the same method as in Example 1, it was found that the film itself was broken by a load of 4200 g / inch width and there was sufficient adhesive force between the brass plate and the PFA film. confirmed.

Subsequently, the electret laminated sheet was cut into the same size as in Example 1, polarized and charged, and then subjected to an aging treatment. After exposing the electretized laminate in the same manner as in Example 1, the residual potential was measured, but almost no charge decay was observed.

Example 3 As a metal sheet, a titanium plate (JIS type 2) having a plate thickness of 0.3 mm was degreased with trichloroethylene and dried, then the plate surface was treated with an aminosilane coupling agent and dried at 100 ° C.

F with a thickness of 12.5 μm and a melting point of 270 ° C as a thermoplastic resin film
Prepared EP film.

The prepared titanium plate and FEP film were thermocompression bonded by being passed between the rolls of the pressure roll used in Example 1 under the conditions of a contact band width of 5 mm, a contact time of 1.5 seconds and a heating roll surface temperature of 330 ° C. After allowing the resulting electret laminate sheet to cool naturally, the thickness of the FEP film layer was measured in the same manner as in Example 1 to find that it was 12.0 μm, and the original thickness of the film used was almost maintained. This film thickness was evenly distributed over the entire surface of the obtained electret laminate sheet, and a smooth and beautiful surface was obtained without air entrapment. The surface roughness of the surface was Ra = 0.2. Next, the adhesive force between the titanium plate and the FEP film was measured by the same method as in Example 1. The film itself was broken by a load of 700 g / inch width, and there was sufficient adhesive force between the titanium plate and the FEP film. It was confirmed.

Subsequently, the electret laminated sheet was cut into the same size as in Example 1, polarized and charged, and then subjected to an aging treatment. After exposing the electretized laminate in the same manner as in Example 1, the residual potential was measured, but almost no charge decay was observed.

Comparative Example 1 The aluminum plate used in Example 1 was treated with tetrafluoroethylene-
A propylene hexafluoride (FEP) copolymer dispersion was spray-coated on a target having a thickness of 25 μm, and baked at 370 ° C. for 20 minutes. When the thickness of the formed film was measured in the same manner as in Example 1, the center value of the film thickness was 25 μm, but the variation range R was as large as 5 μm, and the fine waviness on the film surface peculiar to the coating was observed. The surface was lacking in smoothness. The surface roughness of the surface was Ra = 1.9. Further, when the adhesive force between the aluminum plate and the film was measured by the same method as in Example 1, it was 1000 g / inch width and the peeling phenomenon was relatively small.

Then, the laminated plate was cut into the same size as in Example 1, polarized and charged, then subjected to aging treatment, and exposed under the same conditions as in Example 1 to measure the residual potential.
The potential dropped to 70% of the initial level, and the decay of the electric charge was observed.

Comparative Example 2 A brass plate (C2680-PH) with a plate thickness of 0.5 mm as a metal sheet
Was degreased with an alkaline solution, and a FEP film having a thickness of 25 μm and a melting point of 270 ° C. was prepared as a thermoplastic resin film. The FEP film was contacted on a brass plate and baked at a temperature of 350 ° C. After allowing the resulting laminated sheet to cool naturally, the thickness of the FEP film layer was measured in the same manner as in Example 1 and found to be 18 μm, which was 72% of the original thickness of the film used. In addition, since the film layer was entirely melted, fine undulations on the surface were observed as in the coating layer of Comparative Example 1, and the surface was lacking in smoothness. The surface roughness of the surface was Ra = 1.5. Further, when the adhesive force between the brass plate and the FEP film was measured by the same method as in Example 1, the film was peeled off under a load of 800 g / inch width.

Next, the laminated sheet was cut into the same size as in Example 1, polarized and charged, then subjected to aging treatment, and exposed under the same conditions as in Example 1 to measure the residual potential. Has decreased to 80% of the initial value, and charge decay has been observed.

Comparative Example 3 The titanium plate and the FEP film used in Example 3 were overlaid, and pressure molding was performed at a temperature of 350 ° C. for 10 minutes by hot pressing. After allowing the resulting laminated sheet to cool naturally,
When the thickness of the FEP film layer was measured in the same manner as in Example 1, it was 8 μm, which was reduced to 64% of the original thickness of the film used. In addition, the surface of the film was often entrained with air, and the surface was lacking in smoothness. The surface roughness of the surface was Ra = 2.0. Further, the adhesive force between the titanium plate and the FEP film was measured by the same method as in Example 1, and it was 600 g / inch width, and the peeling phenomenon was relatively small, but the variation depending on the location was observed.

Then, the laminated sheet was cut into the same size as in Example 1, polarized and charged, then subjected to aging treatment, and exposed under the same conditions as in Example 1 to measure the residual potential. It decreased to 65% of the initial level, and the decay of electric charge was observed.

Claims (4)

[Claims] 1. A heat capable of supplying a metal sheet to the heating roll side and forming an electret on the roll side having no heating source, of a pressure-bonding roll composed of a pair of a heating roll and a roll having no heating source. While supplying the thermoplastic resin film, insert the metal sheet and the thermoplastic resin film between the rolls, the contact time between the metal sheet and the thermoplastic resin film and the roll is 1 to 10 seconds, the contact band width is 1 to 20 mm.
The method for producing an electret, wherein the laminate is obtained by thermocompression-bonding the both, and charging the laminate. 2. The method according to claim 1, wherein the metal sheet is a plate selected from aluminum, stainless steel, copper, titanium and alloys thereof. 3. A thermoplastic resin film having a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkoxyethylene copolymer, a tetrafluoroethylene-ethylene copolymer, a tetrafluoroethylene. The method according to claim 1 or 2, which is a film selected from polymers, polypropylene and polycarbonate. 4. The method according to any one of claims 1 to 3, wherein the surface temperature of the heating roll is in the range of -20 ° C to + 80 ° C from the melting point of the thermoplastic resin film.